High-temperature tungsten base alloys



United States Patent 3,150,971 HlGH-TEMPERATEHKE TUNGSTEN BASE ALLOYS Edward D. Weisert and Roger A. Perkins, Tonawanda,

and Doyle Geiselrnan, Kenmore, N.Y., assignors to Quinn Carbide (Importation, a corporation of New sari; No Drawing. Filed Feb. 25, 1959, Ser. No. 795,320

2 Claims. Ci. 75-176) This invention relates to tungsten-columbium-base alloys suitable for use at high temperatures.

The ever-increasing demands of industry for stronger and more heat resistant materials of construction have spurred research in the metals and alloys field. Recent developments in the fields of rocketry and gas turbine engines, for example, have provided designs for apparatus requiring exceptional performance characteristics in their structural components. The high strength-high temperature metals field has been called upon to provide metals and alloys sutiable for use in these new devices. Old metals and alloys have been improved and new alloys are avidly being sought to provide materials capable of withstanding high stresses at ultrahigh temperature for extended periods of time.

The present high temperature alloys are iron-, nickel-, and cobalt-base alloys. These alloys have excellent strength characteristics within speeii c temperature ranges but use of these materials is severely limited at temperatures above 1800 F. and the alloys are wholly inadequate at the ultrahigh temperatures of operation in the 2400 F. to 3500 F. range that is demanded toway. The deficiencies are especially evident when the alloys are subjected to high stresses at ultrahigh temperatures.

Tungsten has long been known as a possibly useful metal for high temperature applications since tungsten possesses the highest melting point (3410 C.) of any metal in the Periodic Table. However, exploitation of tungsten or the other high melting point refractory metals, such as columbium and tantalum, has been seriously limited by their extremely poor resistance to oxidation at high temperatures. When exposed to air at 1040 C. for a period of 24 hours, a specimen of tungsten was oxidized almost completely-the actual weight gain due to oxidation was 1235 mg. per cm.

The primary object of the invention, therefore, is to provide a complex tungsten-columbium base alloy which is characterized by superior oxidation resistance at ultrahigh temperatures.

Another object of this invention is to provide a wide variety of tungsten-columbium-base alloys which, in addition to having excellent oxidation resistance, also exhibit superior high-temperature properties and corrosion resistance.

Other aims and advantages of the invention will be apparent from the following description and appended claims.

In accordance with the present invention an alloy is provided containing from 50 to 95 percent by weight tungstem and from 5 percent to 50 percent by weight columbium.

To this binary-base alloy may be added one or more modifying metals in the following ranges: from G to 45 percnt by weight in the aggregate of chromium, tantalum, titanium, vanadium, molybdenum, zirconium and hafnium, from 0 to 40 percent by weight in the aggregate of iron, nickel, cobalt and manganese, from O to 12 percent by weight aluminum, from O to 2 percent by weight boron, and from 0 to 5 percent by weight in the aggregate of one or more elements selected from the group consisting of the rare earth metals, yttrium, scandium, calcium, silicon, and magnesium. The total amount of these modifying metals which may be added to the tungstencolumbium-base should not exceed 45 percent by weight.

In a preferred embodiment, the alloy contains at least 50 percent tungsten and from 10 to 50 percent columbium with the modifying metals present in the following ranges: from 0 to 40 percent by weight in the aggregate of chromium, tantalum, titanium, vanadium, molybdenum, zirconiu and hafnium, from 0 to 30 percent by weight in the aggregate of iron, nickel, cobalt and manganese, from 0 to 5 percent by weight aluminum, from 0 to 2 percent by weight boron, and from 0 to 5 percent by weight in the aggregate of one or more elements selected from the group consisting of the rare earth metals, yttrium, scandium, calcium, silicon and magnesium. The total amount of these modifying metals which may be added to the tungsten-columbium-base should not exceed 40 percent by weight of this preferred embodiment of the alloy.

Carbon, oxygen and nitrogen may be present in a combined amount not exceeding 2 percent by weight, but best results are obtained when they are limited to a maximum of one percent.

By allowing tun sten with columbium, a binary composition is formed which overcomes a great number of the undesirable characteristics of pure tungsten and yet retains the more desirable characteristics. For example, by alloying tungsten with from 5 percent to 50 percent by weight columbium, up to a IOU-fold improvement in oxidation resistance may be obtained. Furthermore, columbium does not form brittle compounds with tungsten. These two elements are mutually soluble in the solid state. The presence of columbium also imparts additional strength over that possessed by pure tungsten. Furthermore, a sizeable addition of columbium will greatly reduce the density of the alloy.

By alloying the tungsten-columbium-base composition with one or more of the high-melting point reactive elements, chromium, tantalum, titanium, molybdenum, vanadium, zirconium and hafnium in the percentage ranges stated, alloys are capable of being formed which exhibit even greater oxidation resistance at temperatures above 1000 C.

The addition of one or more metals from the group consisting of iron, nickel, cobalt and manganese in the ranges stated also gives alloys having greater oxidation resistance and which still retain the inherent high strength and corrosion resistance of tungsten and tungsten base alloys. These additions also serve to lower the density of the alloy.

Addition of aluminum in amounts up to 12 percent by weight will increase oxidation resistance and lower the density, an important consideration where high strength and low weight structural materials are required.

Boron may be added up to two percent by weight to further enhance the overall properties of the alloy of the invention.

Furthermore, the addition to the alloy of One or more elements from the group consisting of the rare earth metals and the elements yttrium, scandium, calcium, silicon, and magnesium will improve the oxidation resistance of the alloys. It has also been found that addition of these metals will improve the mechanical properties of the alloys. For these reasons up to 5 percent in the aggregate of these elements may be added to the alloy.

The total amount of these secondary elements added to the tungsten-columbium-base alloy must be limited to 45 percent by weight of the tungsten-columbium base and 40 percent for the more specific embodiment, .for additions of secondary metals in amounts exceeding these percentages reduces the amount of high strength primary metals present.

The overall properties of the alloys of the invention are dependent, to some degree, on the impurity content of 3 the individual constituents since such impurities may be transferred to the alloy. Therefore, it is recommended that high purity materials be employed to form the alloys. However, a total of up to one percent metallic impurities will not materially affect the properties of the alloys.

Carbon, oxygen, and nitrogen may be present in a combined amount not exceeding two percent by weight, but the best results, particularly with respect to workability, are obtained when the total amount of these impurities does not exceed one percent.

Alloys which fall within the compositions defined above may be prepared in an arc-melting furnace having consumable or non-consumable electrodes. These alloy may also be prepared by any powder metallurgical technique, as for instance, extruding, slip casting, or hotor coldpressing, by induction melting or by any other method, provided some precaution may be exercised to protect the hot metal from contamination by air.

The superior oxidation resistance of the alloy of the invention was substantiated experimentally. An alloy containing 85 percent by weight tungsten and percent by weight columbium was prepared by melting together the required amounts of the two constituents in a nonconsurnable electrode, inert-gas-shielded, arc-melting furnace. Complete homogeneity of the alloy was ensured by repeatedly remelting the button until material suitable for testing was obtained. A specimen wa machined from the cooled product of this furnace and tested for resistance to oxidation. The specimen was weighed and then heated in a muffie furnace at a temperature of 1040 C. for a 24 hour period, after which it was weighed again to determine the weight gain due to oxidation.

Under these conditions the alloy showed a weight gain of 103.20 mg. per cmfi. Unalloyed tungsten tested under similar conditions showed a weight gain of 1235 nag/ch1 Comparison of these results shows a greater than lihfold improvement in oxidation resistance by use of the tungstcnrcolurnbium binary base alloy of this invention. By the addition to the tungsten-columbium base of the moditying metals Cr, Ta, Ti, V, Mo, Zr, Hf, Fe, Ni, Co, Mn, Al and B in the ranges specified even greater oxidation resistance can be achieved. Table 1 shows the Weight gain due to oxidation at a temperature of 1040 C. for a 24 hour period, for several alloy compositions. These alloys were produced and tested under the same conditions as the example given above.

Table 1 Composition, percent by weight Weight gain due to oxidation, rug/cm). W 013 Other 85 15 103. 60 362. 40 60 15 31. 21 60 15 26. 60 15 20Ni-5Mo 15. 70 60 18 20Ni-2V 151. 20 5O 20 2OFo-l01a 166. 80 50 20 ZOFe-SJZCo-LSTa. 21. 40 50 20 20Fe-8ATa-L6B 17. 60 50 3O 10Fe100r 98. 50 50 30 10Ni-l00r 23. 60 50 20 1OFc-200r 6. 77 50 20 1ONi20Gr 24. 00 50 10 10Fe-30Cr. 5. 99 50 10 IONi-300r 11. 8O 60 20 15Cr-5A1 126. 70

In another experiment, pure tungsten and a percent tungsten-3'0 percent columbium alloy was tested at a temperature of 1200 C. in an atmosphere of dry oxygen. The gain in weight due to oxidation was recorded in a continuous weighing process. After hours it was found that the sample of pure tungsten had undergone a weight gain of 60,000 nag/cm. while the alloy sample had undergone only a 485) rug/cm. weight gain. This represents a greater than IOU-told improvement in oxidation resistance.

By comparing the results obtained in the pics with those obtained for pure tungsten, the vast improvement in oxidation resistance which characterizes tungsten-columbium-base alloys is immediately evident.

The addition of columbium to tungsten also serves to produce alloys of greater hardness and strength than pure tungsten. This was corroborated in hardness tests conducted on two compositions of the columbium-tungsten alloy and one specimen of pure tungsten. The results of these tests are shown in Table 2.

above exam- It is seen, therefore, that the alloy of this invention constitutes an important advancement in high temperature technology. Possessing the high strength corrosion resistance inherent in tungsten, as well as increased oxidation resistance and workability, these alloys may be fabricated into complex structural forms and sheets to be used at high temperatures for extended periods of time.

What is claimed is:

1. An oxidation resistant alloy for use at high temperatures consisting essentially of about 16 percent columbiurn, about 30 percent chromium, about 19 percent iron, and the balance tungsten and incidental impurities.

2. An oxidation resistant alloy for use at high temperatures consisting essentially of about 20 percent by weight columbium, about 20 percent by weight chromium, and about 10 percent by weight iron, and the balance substantially all tungsten and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 1,520,794 Zone Dec. 30, 1924 1,893,144 Kropf Jan. 3, 1933 2,122,403 Balke et al July 5, 1938 FOREIGN PATENTS 888,708 France Sept. 13, 1943 

1. AN OXIDATION RESISTANT ALLOY FOR USE AT HIGH TEMPERATURES CONSISTING ESSENTIALLY OF ABOUT 10 PERCENT COLUMBIUM, ABOUT 30 PERCENT CHROMIUM, ABOUT 10 PERCENT IRON, AND THE BALANCE TUNGSTEN AND INCIDENTAL IMPURITIES. 